The invention generally relates to a controlled meter valve flow system and more particularly relates to an electronically controlled meter valve flow system.
During the course of loading large reservoirs, such as tank trucks for example, with a fluid material problems arise at initial loading, i.e. splashing and vapor generation; and, again during the shutdown cycle from shock waves in the system due to high flow rate at or near full capacity.
Special fluid flow networks have been devised to assist in loading these reservoirs without undue splashing, vapor generation or shock. Flow network systems that are generally used for filling large reservoirs such as tankers may be generally referred to as load rack systems. Presently, in the load rack systems globe valves are used to stop fluid flow into the reservoir. This shutdown is presently accomplished with a series of pilot valves associated with the globe valves which are hydraulically actuated. In order to actuate the pilot valves there must be a pressure drop across the globe valve of approximately 8-10 psi. Once the pilot valves are actuated in a predetermined sequence the flow rate will be decreased to one final rate then shut off.
Many problems have arisen in the use of the pilot valves including freezeups due to the many secondary loops to the main globe valve, wear of the pilot valves, high maintenance costs, and difficulty of adjustments which are critical to the overall operation of the globe valve.
In order to determine the volume going through the fluid flow network or load rack a turbine meter is often utilized to determine flow rate and volume. The range of the turbine meter is limited to between 100 and 1000 gallons per minute.
Positive displacement meters (PDM) are also utilized in determining volume through a fluid flow network. The PDM differs from the turbine meter in that it is compartmentalized, which facilitates the determination of volume through the system. Thus, any movement of the shaft within the positive displacement meter is indicative of a specific volume of fluid through the meter. Controlling startup and shutdown of fluid flow networks have been accomplished using globe valves with pilot valve controls whereby the volume or flow rate is determined in either a turbine meter or a positive displacement meter. The present invention overcomes the problems enunciated above for the pilot valves by eliminating the large pressure drop required in the pilot valve system. This uses less energy from the prime mover, resulting in a more efficient system and lowering the overall operating cost.